If inbound starts at 1, and outbound starts at 23, you can somewhat infer how many channels are simultaneously in use for in or out, but you cannot really infer how many total channels are simultaneously in use, as in/out may peak at different times of day. In my former Executone life, that was one of the standard reports that proved handy time after time. Of course, with most PRI circuits in North America, you get 23 channels - so it really only matters if all are full, at which time you'd likely get a SSA alert on failed outbound attempts.